1. Field of the Invention
The present invention generally relates to concrete pumping apparatus, and more particularly to a shuttle valve having an improved wear ring assembly.
2. Background Information
Concrete pumps have been in use for a number of years and are generally of a common design which utilizes a feed hopper into which wet concrete is dumped. Either attached to the side of the hopper near the bottom of the hopper, or to the bottom of the hopper itself, is a wear plate having at least two openings therethrough. Attached to the other side of the hopper, in alignment with the wear plate openings, are two hydraulic rams which alternately draw wet concrete from the hopper and then alternately pump this concrete through a transmission conduit which is attached to a slidable shuttle valve which alternately aligns and registers with the discharge conduit of the hydraulic ram at the beginning its output throw of the pumping cycle. This type of prior art concrete pumping apparatus is described in U.S. Pat. Nos. 4,198,193 and 4,337,017, the teachings of which are herein incorporated by reference.
The problem is, as can be seen in the incorporated prior art references, there is a slidable plate, commonly called the nun plate which slides back and forth over the two openings in the wear plate. A seal must be provided between the slidable plate and the wear plate in spite of the fact that wet concrete is a very abrasive substance. The seal between the slidable plate and the wear plate is normally provided by a wear ring which acts as a seal with the wear plate and a shear-type guillotine valve to push aside or cut through the mixture of concrete as it opens up each cylinder alternately to either the hopper or the pressure outlet. This requires a predetermined contact pressure between the wear ring and the wear plate which is compromised by any wear between these parts. In fact, the environment is so abrasive that the contact between the wear ring and the wear plate is only ideal for the first few hours of operation. There is constant wear and degradation that is only corrected by new parts or by continuous mechanical adjustment. If an operator fails to continuously mechanically adjust the seal between the wear ring and the wear plate, the rate of degradation increases as the wear occurs since more of the abrasive wet concrete can be found between the wear ring and the wear plate. Failure to maintain a proper seal will result in premature failure of the pump as the guillotine action degrades and the leaking wet concrete wears out the wear plate and the seal. This is an especially acute problem with mechanical type adjustments such as set screws and the like, since not all pump operators are as conscientious as others and will oftentimes overlook the need to readjust or replace the wear ring as needed.
In the prior art, others have attempted to use hydraulic pressure either from the wet concrete itself, or hydraulic fluid as a means of sealing. However, this has not proved satisfactory in that the environment is so abrasive that wet concrete does not provide an adequate seal, and the hydraulic systems are subject to leaks which contaminates the concrete.
Accordingly, it is an object of the present invention to provide a means of spring loading the wear ring against the wear plate in order to provide a continuous, automatic, adjustment of the position of the wear ring relative to the wear plate as the wear ring is abraded away.
Additional objects, advantages and novel features of the invention will be set forth in part in the description as follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
These objects are achieved by use of a shuttle valve which has a wear plate attached to a side wall of a hopper and a pivotal nun plate which pivots about a driven shaft. The wear plate is provided with two annular openings which are aligned and register with the openings to a pair of hydraulic cylinders. Each of the hydraulic cylinders has a hydraulically driven piston which alternately draws wet concrete from the hopper and then alternately pumps this concrete through the annular openings in the wear plate and through a nun plate annular opening into a flexible conduit.
The flexible conduit is bonded to a conduit collar which is attached to the nun plate by means of tap screws. The conduit collar can be formed of a variety of materials but in the preferred embodiment is of a rigid material so as to provide a flanged surface which reduces the size of the nun plate annular opening to one conforming to the annular size of the annular openings in the wear plate. This flange is used to hold a plurality of belleville springs in compression against the wear ring.
A wear ring is provided for slidable engagement against the surface of the wear plate and is held in slidable engagement by means of the belleville springs. In the manner the belleville springs provide constant, automatic adjustment to maintain the original contact pressure between the two wearing parts, namely the wear plate and the wear ring.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive.